Electrolyte for lithium-ion batteries to improve graphite anode surface stability and lithium-ion batteries containing the same

Long-life graphite anode electrolyte forming a phosphorus/silicon-based SEI derived from TMSP additives

This technology enhances battery lifespan and high-temperature stability by adding tris(trimethylsilyl) phosphite (TMSP) to lithium-ion battery electrolytes, creating a stable SEI layer containing phosphorus (P) and silicon (Si) on the graphite anode surface through electrochemical reduction and chemical reaction pathways.

Conventional electrolyte additives like VC often suffer from poor compatibility with high-capacity cathode materials, leading to reduced cycle life and swelling at high temperatures. Furthermore, the non-uniform formation of the SEI layer has historically caused continuous electrolyte decomposition.

This technology utilizes 3 wt% TMSP relative to the total electrolyte weight, combined with an ethylene carbonate (EC) and ethyl methyl carbonate (EMC) mixed organic solvent, to form a chemically modified SEI layer on the anode surface that exhibits specific peaks in XPS and 31P-NMR analysis. This electrolyte is suitable for EV pouch cells using graphite anodes and energy storage system cells exposed to high-temperature environments, offering a specific capacity retention of over 95% after 50 cycles.

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Key Features:

• A lithium-ion battery cell comprising a cathode, a graphite anode, an electrolyte for lithium-ion batteries, and a separator
• An electrolyte containing 3 wt% of a TMSP compound represented by Chemical Formula 1, along with an organic solvent and a lithium salt
• An organic solvent that dissolves the lithium salt within the electrolyte, consisting of ethyl methyl carbonate (EMC) and ethylene carbonate (EC) in a 2:1 volume ratio
• An anode surface SEI layer exhibiting peaks at F1s 685.3 eV, P2p 134.8 eV and 130.9 eV, and Si2p 101.9 eV in XPS analysis, and an R-P(=O)-(OR)2 peak in 31P-NMR

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